1. Field of the Invention
The present invention relates to developing devices, image forming apparatuses, image forming systems, charging members, and methods for manufacturing developing devices.
2. Description of the Related Art
Image forming apparatuses such as laser beam printers are well known. Such image forming apparatuses include, for example, an image bearing member for bearing a latent image, and a developing device for developing the latent image borne by the image bearing member with a developer. When the image forming apparatus receives image signals etc. from an external device such as a host computer, it positions the developing device at a developing position which is in opposition to the image bearing member, develops the latent image borne on the image bearing member with the developer contained in the developing device to form a developer image, and transfers the developer image onto a medium to ultimately form an image on the medium.
This developing device further includes, for example, a developer bearing member for bearing the developer, and a charging member that is placed in contact with the developer bearing member for electrically charging the developer borne by the developer bearing member. (See, for example, JP 2000-214659A.)
(1) This charging member includes a conductive agent for providing the charging member with conductivity. Furthermore, in order to electrically charge the developer borne by the developer bearing member with the desired charge amount, it is necessary to disperse, as a whole, a sufficient amount of conductive agent throughout the charging member.
On the other hand, when looking at the portion where the charging member is placed in contact with the developer bearing member, it can be seen that the more the developing device is used, the more of the surface contacting the developer bearing member is worn off, and the more of the conductive agent is exposed. In this case, a decrease in the charge amount of the developer is promoted due to the developer contacting the exposed conductive agent. Moreover, when the charge amount of the developer decreases too much, there is a possibility that developer with little charge amount is borne by the developer bearing member, and fogging may occur.
(2) Moreover, the charging member may be formed by centrifugal molding, in which the material of the charging member is supplied into a hollow die having an inner wall, and the die is rotated, thus molding the charging member. In this case, a portion in which the developer is dispersed will be formed in the charging member on the side that is proximate to the inner wall of the die and a portion where almost no developer is present will be formed in the charging member on the side that is distant to the inner wall, due to the centrifugal force during the molding. Moreover, at the boundary between these two portions, the conductive agent is dispersed non-uniformly.
In conventional developing devices, the surface on the side distant from the inner wall is placed in contact with the developer bearing member. In this case, there is a possibility that the developer is charged non-uniformly, and stripes may appear in the developer image formed on the image bearing member.